Gage control system for hot rolling mills

ABSTRACT

Described is a workpiece gage control system for a hot rolling mill, intended for use as an adjunct to existing gage control systems, which measures the temperature of incoming end of the workpieces and compares this with the temperature of the incoming end of the previous workpiece and the gage of the forward end of the previous workpiece. Assuming that a screwdown correction is required, this comparison results in a control signal which adjusts the screwdown setting of the mill to maintain output gage substantially constant regardless of temperature variations.

United States Patent Gillstrom GAGE CONTROL SYSTEM FOR HOT ROLLING MILLS[72] Inventor: Robert B. Gillstrom, Malvern, Pa.

[73] Assignee: Westinghouse Electric Corporation,

Pittsburgh, Pa.

[22] Filed: April 30,1970

[2]] Appl. No.: 31,842

Related US. Application Data [63] Continuation of Ser. No. 715,051,March 21,

1968, abandoned.

521 U.s. Cl ..72/9, 72/13 [51] Int. Cl. ..B2lb 37/10 [58] Field ofSearch ..72/6, 13

[56] References Cited UNITED STATES PATENTS 3,186,201 6/1965 Ludbrook etal. ..72/9 3,044,330 7/1962 Roberts ..72/200 3,111,046 11/1963 Koss etal ..72/15X LOAD CELL TEMPERATURE I DEVICE I 62 s4 s1 69 LOAD LOAD CELLCELL E DELAYED LOGIC I151 3,691,801 [451 Sept. 19, 1972 OTHERPUBLICATIONS Automatic Gage Control for Modern l-lot Strip MillsWallace, Dec. 1967, Iron & Steel Engr. pp. 75- 86.

Primary Examiner-Milton S. Mehr Attorney-F. l-l. Henson and R. G.Brodahl [5 7] ABSTRACT Described is a workpiece gage control system fora hot rolling mill, intended for use as an adjunct to existing gagecontrol systems, which measures the temperature of incoming end of theworkpieces and compares this with the temperature of the incoming end ofthe previous workpiece and the gage of the forward end of the previousworkpiece. Assuming that a screwdown correction is required, thiscomparison results in a control signal which adjusts the screwdownsetting of the mill to maintain output gage substantially constantregardless of temperature variations.

8 Claims, 1 Drawing Figure X-RAY 9 g GAGE I HEAD 48 MEMORY RESETSCREWDOWN 54 CONTROL 5& I4

GAGE CONTROL SYSTEM FOR NOT ROLLING MILLS This is a continuation ofapplication, Ser. No. 7 l 5,05 l filed Mar. 21, 1968, now abandoned.

BACKGROUND OF THE INVENTION In hot rolling mills, such as bar mills, theincoming workpiece passes through a number of stands before its gage orthickness is measured as it emerges from the last stand. If the actualmeasured gage deviates from the desired gage, the screwdown settings ofthe various stands are adjusted, but by this time a considerable lengthof off-gage product has passed through the mill. The problem iscomplicated by the fact that regardless of the desired gage setting ofthe mill, the actualgage will vary with the temperature of theworkpiece. That is, hotter, and consequently softer, workpieces willtend to be reduced to a greater degree than cooler workpieces;

Temperature variation from one workpiece t'o the next can result fromvarious factors. For example, skid marks from the water cooled skids inthe preheat furnace are a source of temperature variations. Also, theworkpiece may be held up in the rolling schedule for a time long enoughto cause the temperature to vary from bar-to-bar, and the spray at thedescaler can cause the head of the workpiece to be colder or hotter thanis controlled by the first stand speed; whereasthe speed of the head iscontrolled by the approach table speed. Similarly, temperaturevariations occur due to differences between furnaces, and the speedsthrough which a pusher is moving the workpieces through the furnace. Inshort, it is exceedingly difficult to maintain all succeeding workpiecesin a single order to have the same temperature characteristics.

SUMMARY OF THE INVENTION provide a control system of the type describedwhich measures the temperature of a workpiece as it passes between thefirst and second stands of a tandem mill, and compares this temperaturewith the temperature of the previous workpiece and the actual gage ofthe previous workpiece to adjust the screwdown setting of the mill.

1 the body. This latter effect occurs since the body speed as anelectrical signal, is applied to the other of the two integrators whereit is stored. Atthe same time, the stored temperature of the head end ofthe workpiece is compared with'( l) the temperature of the head end ofthe workpiece previously passing through the mill and (2) the gage ofthe head end of .the workpiece previously rolled. Assuming thatasci'ewdown correction is required, this comparison produces an errorsignal for adjusting the mill screwdown.

If, for example, the firstworkpiece is on gage, and the followingworkpiece is detected to be colder than the first, the mill screw willrun down while the bar is in the mill to compensate for this deviationand'givc the bar a gage closer to the first one. If the head of thefirst bar is not on gage, an electrical signal proportional tothe'off-gage condition is-compar'ed with the temperatures of the firstand second bars, respectively, to make the second workpiece on gage bythe combination of the deviation of the first workpiece and thetemperature variation.

Further, in accordance with the invention, the temperatures of the headends of the workpieces are sampled for about 2 seconds, and thesetemperatures, in

the form of electrical signals, are stored in the aforesaid integrators.However, such integrators will store the electrical signalsproportional-to temperature no longer than about 3 to 4 minutes.Accordingly, passage of the end of a given workpiece through the laststands in the tandem mill is recorded; and if no succeeding bar ispassed through the mill within a period of 3 to 4 minutes, thetemperatures comparison step is not made as before described. Rather,the screwdown is reset, and only a succeeding bar can begaged by thetemperature measurement system as described above.

The above and other objects and features of the invention will becomeapparent from the following detailed description taken in connectionwiththe accompanying single FIGURE drawing which schematically illustratesone embodiment of the invention. v

With reference now to the drawing, a tandem hot rolling mill isshowncomprising a plurality of rollingmill stands 81-86. A' workpiece l0,heated to an elevated temperature, is shown passing through the stands81-86. As was explained above, the amount of reduction taken on theworkpiece 10 and, hence, its issuing gage is a function of itstemperature. For a given screwdown setting, a workpiece of a giventemperature In accordance with the invention, a temperature will besofter and its final gage less than that of a colder workpiece,assuming, of course, that they have the same metallurgical composition.As the strip issues from the last stand S6, its gage is measured by athickness measuring X-ray gage 12, such as an X-ray gage. This gage isapplied as an electrical signal to a screwdown control circuit 14 forthe rolling mill; and is also fed to a head memory unit 16 which storesthe gage of the forward end or head section only of the workpiece. I

Once the workpiece 10 emerges from the last stand S6, its thickness canbe measured by the gage l2 and the spacing between the rolls of the millcontrolled by the conventional screwdown control circuit 14. However, bythe time that the forward end of the strip reaches the gage 12, aconsiderable amount of material has passed through the mill which may beoff-gage due.

to a difference in temperature from the preceding workpiece.

lnaccordance with the present invention, a tempera ture sensing,ormeasuring device 18, such as an infrared pyro'me'tefl-is positionedbetween thefirst and an electricalsignal, is applied via lead andresistor 21 to an isolation amplifier 22 having a resistive feedbackpath 23. The temperature measuring device 18 A has a separate powersupply, not shown, and the isolation amplifier has a high inputimpedance to match that of the device 18. The output of the isolationamplifier,

CRLA to asecondintegrator-26. Each integrator 24 or i 2 is provided witha feedback. capacitor 28', .the

' proportionaljto the temperature of the strip is applied throughisolation amplifier 22 to integrator 26. On the other hand, whenrelayCR2 is energized and'relay-CRl deenergized, the electrical signalproportional'to tem- -(i.'e'., that stored in integrator 26). c a tum,can PP gh contacts Q a .These' temperatures are also compared with thehead first integrator 24, or through a second set of contacts.

ingworkpiece is rolled and its forward end reaches the stand S2, relaysCR2 and CR3 will be energized momentarily, along with relay CR4 which isenergized momentarily each time a workpiece enters stand S2. However,relays CR] and CR5 will remain deenergized.

It ,can be seen, therefore, that as. one workpiece is being rolled andrelays'CRl and CR5 are energized, for example, the temperature 1 of .theworkpiece being rolled is stored in integrator 26. When the nextworkpiece is rolled, howeverQrelays CR2 and CR3 areenergized, .Thispermits storage-of the temperature of the workpiece being rolled inintegrator 24. At the same time,-since contacts CR4-A are closed, theactual temperature of the workpiece now being rolled is compared-withthetemperature of the previous memory from storage circuit 16.; Thus,assuming that the head of the previous workpiece was on gage, theetectrical signal passing through contacts CR4- A and proportional tothe temperature of the 'workpiecenoiw being rolled is simply comparedwith that proportional to the temperature of the preceding workpiecepassing through contacts CR3 -A. lf,.h'owever, the gage of the head ofthe previous workpiece was above or below the desired gage, thesignalappliadto the amplifier 38 is Y modified by thehead memory signal.The signal passing perature is applied the integrator 24. All of therelays I shown herein arepreferably of the mercury wetted type, thesymbols used in the'drawing being for illustrative purposes only. a

pears across resistor 40 and is applied via movable-tap 42, contactsCRS-jA of relay CR5 and resistor 44 to the 7 input of amplifier 38. Alsoapplied to the input of amplifier 38 via contactsCR4-A of relay CR4andresistor amplifier 38. Similariy, the output of integrator 24apthrough contacts CR4-A is compared 'in subtractive relationship withthat passing through contacts CR3-A or CR S-A from the integrators,respectively. That is, if the signal proportional to the measuredtemperatureof the workpiece passing through the mill is equal to that ofthe previous workpiece, then no corrective signal is sent: to thescrewdown control,.assumingalso that the output of the head 'memoryunit'l6 is zero, indicating that the actual gage of the precedingworkpiece was of the mill.

46 is the electrical signalproportional to the temperature of theworkpiece presently in themill. That is, the signalappliedthroughcontacts CR4-A is that" due to the temperature of the workpiecebeing rolled; whereas those from the integrators 24 or 26 arerepresentative appears across resistors 54 and 56; resistor 54 having ar movable tap 58 thereon connected through a feedback resistor .60 tothe input of the amplifier 38. The output I from amplifier 38 appearingacross resistors 54 and 56.

is then applied to the screwdown control circuit 14.

. In the operation of the system shown the drawing, and as willbeexplained hereinafter in detail, the relays CR1 and CR5, for example,will be energized momentarily, on the order of about 2 seconds, as soonas the forward end of a-first workpiece being rolled enters the standS2. At the same time, the relay CR4 will be energized to close itscontacts CR4-A; however relays CR2 1 and CR3 will be deenergized. Whenthe next succeedit now remains to be explained how the relays areactuated in the desired sequence. Means are provided for sensing thepassage of thestrip through stands 81, S2, S5 and S6. This may comprise,for example, strain gages or roll force load cells 62 and 64 on stands81 and S2 and strain gages 67 and 69 on stands S5 and S6, respectively.The signals produced by the strain gages 62 and 64 are applied to alogic module, preferably an AND circuit 66; and assuming thatthe stripis inboth stands S] and S2, the AND module 66 produces an output whichis inverted ininverter 68 and applied to AND logic module 70. At thesame time, the output of AND module 66 is applied through a 2-seconddelay circuit veoritaets CR4-A.

When the strip is in stands 81 and S2, the signals from strain gages 62and 64-are applied to-AND logic module 82 which, through inverter 84,causes a flipflop circuit 86 to reverse its stable states of conduction.In one stable state of conduction, AND logic module 88 is activated;whereas, in the other stable state of conduction, AND logic module 90 isactivated. Assumworkpiece ing that AND logic module 88 is activated, theoutput of ANDmodule 70 persisting for 2seconds when the strip enters thesecond stand S2 causes an output signal from AND module 88 to passthrough inverters 92 and 94 to momentarily energize, through leads 96and 98, the relays CR2 and CR3. Under these circumstances, thetemperature signal from theprevious workpiece stored in integrator 26 iscompared with that from the workpiece then passing through the mill; andat the same time the temperature from the workpiece passing through themill is stored in integrator 24.

When the next successive workpiece passes through stand S1 and entersstand S2, the flip-flop 86' will reverse its stable states ofconduction, thereby activatingthe AND logic module 90. Now, when thetwosecond signal appears at the output of module 70, and the AND logicmodule 88 will block the signal; however the module 90 will pass itto-two inverters 100 and 102. The output of inverter 100 is utilized vialead 104 to energize relay CR5; whereas the output of module 102 isapplied via lead 106 to energize the relay CR1. Thus, on this succeedingworkpiece, relays CR1 and CR5 are energized momentarily for about 2seconds; whereas relays CR2 and CR3 remain deenergized. The relay CR4,of course, is always energized upon passage of each workpiece throughthe mill. V

The strain gages 67 and 69 sense the passage of the trailing end of theworkpiece through the mill. Signals indicating the passage of theworkpiece through the mill are applied to a logic circuit 108 includinga signal memory function such as the charging of a capacitor to blockthe circuit and which will produce an output signal on lead 110,assuming that no preceding workpiece has passed through the mill in aperiod of 3 to 4 minutes. Under these circumstances, AND logic module112, upon receipt ofthe 2-second signal from module 70, will produce asignal which is inverted in inverter 114 and applied to relay CR6 whichcloses its contacts CR6-A to reset the screwdown control circuit 14.This is for the reason that in the 3 to 4 minute delay interval, thesignal proportional to temperature stored in the integrator 24 or 26 hasbeen dissipated. Consequently, any attempt to compare actual temperaturewith the stored temperature would give erroneous measurements. Y

The present invention thus provides a means for measuring thetemperatures of successive workpieces rolled on a hot rolling mill andfor changing the screwdown setting of the mill based upon a comparisonof the temperature of a workpiece measured and that of a previousworkpiece, this comparison preferably being taken in combination with ameasurement of the gage of the previous workpiece. Although theinvention has been shown in connection with a specific embodiment, itwill be readily apparent to those skilled in the art that variouschanges in form and arrangement of parts may be made to suitrequirements without departing from the spirit and scope of theinvention.

I claim as my invention:

1. In a rolling mill workpiece gage control system, the combination ofsignal producing means for producing respective electrical signalsproportional to the temperature of the forward ends of successiveworkpieces passing through the rolling mill, storage means for storingeach of said electrical signals for a predetermined time period relatedto the passage of said workpieces, comparison means operable when thetemperature of the forward end of a given workpiece is measured withinsaid time period for comparing the signal proportional to thetemperature of said given workpiece with the signal proportional to thetemperature of a preceding workpiece to produce an error signal relatedto a predetermined comparison of said signals, and control meansresponsive to said error signal for controlling said workpiece gage,said storage means for storing said electrical signals comprises a pairof integrators, first switch means actuable when a workpiece passesthrough said mill for connecting one of saidintegrators to said signalproducing means while connecting the other integrator to said comparisonmeans, and second switch means actuable when the next successiveworkpiece passes through said mill for connecting the other of saidintegrators to said signal producing means while connecting said oneintegrator to said comparison.

2. The control system of claim 1 wherein said rolling mill comprises atandem mill having a plurality of rolling stands, means for sensingpassage of the forward end of a workpiece through the second of saidstands, means responsive to said sensing means upon passage of aworkpiece through the second stand for closing said first switch meanswhile maintaining said second switch means open, and means responsive tosaid sensing means for closing said second switch means whilemaintaining the first switch means open upon passage of the nextsuccessive workpiece through said second stand;

3. The control system of claim 2 including switch means actuable whenthe forward end of a workpiece is in said second stand for connectingsaid signal producing means to said comparison means.

4. The control system of claim 3 wherein each of said switch means isclosed momentarily only after a workpiece passes through said firststand and enters the second stand.

5. The control system of claim 4 including means for sensing the passageof the trailing end of a workpiece through the last stand of saidtandemrolling mill and means responsive to said last-named sensing means andactuable after a predetermined time delay for controlling said workpiecegage by resetting the screwdown control system for said rolling mill.

6. The control system of claim 1 including means for producing anelectrical signal which varies as a function of the gage of the forwardend of a workpiece emerging from said mill, means for storing saidelectrical signal which varies as a function of gage, said means forcomparing signals including means for comparing saidtemperature-proportional signals with said stored electrical signalwhich varies as a function of gage.

7. The control system of claim 6 wherein the latter said storedelectrical signal is proportional to the gage of the forward end of aworkpiece which has passed through the mill immediately preceding theworkpiece passing through the mill during a comparison made by thelatter said signal comparing means.

8. The control system of claim 1 wherein said rolling mill comprises atandem r'nill having a plurality of rolling stands, with said signalproducing means being disposed between the first and second stands.

1. In a rolling mill workpiece gage control system, the combination ofsignal producing means for producing respective electrical signalsproportional to the temperature of the forward ends of successiveworkpieces passing through the rolling mill, storage means for storingeach of said electrical signals for a predetermined time period relatedto the passage of said workpieces, comparison means operable when thetemperature of the forward end of a given workpiece is measured withinsaid time period for comparing the signal proportional to thetemperature of said given workpiece with the signal proportional to thetemperature of a preceding workpiece to produce an error signal relatedto a predetermined comparison of said signals, and control meansresponsive to said error signal for controlling said workpiece gage,said storage means for storing said electrical signals comprises a pairof integrators, first switch means actuable when a workpiece passesthrough said mill for connecting one of said integrators to said signalproducing means while connecting the other integrator to said comparisonmeans, and second switch means actuable when the next successiveworkpiece passes through said mill for connecting the other of saidintegrators to said signal producing means while connecting said oneintegrator to said comparison.
 2. The control system of claim 1 whereinsaid rolling mill comprises a tandem mill having a plurality of rollingstands, means for sensing passage of the forward end of a workpiecethrough the second of said stands, means responsive to said sensingmeans upon passage of a workpiece through the second stand for closingsaid first switch means while maintaining said second switch means open,and means responsive to said sensing means for closing said secondswitch means while maintaining the first switch means open upon passageof the next successive workpiece through said second stand.
 3. Thecontrol system of claim 2 including switch means actuable when theforward end of a workpiece iS in said second stand for connecting saidsignal producing means to said comparison means.
 4. The control systemof claim 3 wherein each of said switch means is closed momentarily onlyafter a workpiece passes through said first stand and enters the secondstand.
 5. The control system of claim 4 including means for sensing thepassage of the trailing end of a workpiece through the last stand ofsaid tandem rolling mill and means responsive to said last-named sensingmeans and actuable after a predetermined time delay for controlling saidworkpiece gage by resetting the screwdown control system for saidrolling mill.
 6. The control system of claim 1 including means forproducing an electrical signal which varies as a function of the gage ofthe forward end of a workpiece emerging from said mill, means forstoring said electrical signal which varies as a function of gage, saidmeans for comparing signals including means for comparing saidtemperature-proportional signals with said stored electrical signalwhich varies as a function of gage.
 7. The control system of claim 6wherein the latter said stored electrical signal is proportional to thegage of the forward end of a workpiece which has passed through the millimmediately preceding the workpiece passing through the mill during acomparison made by the latter said signal comparing means.
 8. Thecontrol system of claim 1 wherein said rolling mill comprises a tandemmill having a plurality of rolling stands, with said signal producingmeans being disposed between the first and second stands.